1. Technical Field
The present invention belongs to the field of animal health and relates to a nucleic acid sequence which comprises the genome of an infectious genotype I (EU) PRRS virus clone. The invention also relates to the use of the nucleic acid sequence of the infectious genotype I PRRS virus clone to study Porcine Reproductive and Respiratory Syndrome (PRRS), a viral disease affecting swine, and in the development of vaccines, therapeutics and diagnostics for the prophylaxis, treatment and diagnosis of PRRS.
2. Background Information
Porcine reproductive and respiratory syndrome virus (PRRSV) is a member of the virus family Arteriviridae and belongs, together with the Coronaviridae, to the virus order Nidovirales. PRRSV is an enveloped virus with a single-stranded, positive-sense RNA genome of about 15 kilobases comprising nine open reading frames (ORFs), namely ORF1a, ORF1ab, ORF2a, ORF 2ab, and ORFs 3 through ORF7. ORFs 1a and 1ab encode large polyproteins that are processed into the viral nonstructural proteins (nsp) by auto- and transcleavages of viral proteases nsp1, nsp2, and nsp4 (Snijder and Meulenberg, 1998).
PRRSV is considered one of the economically most important infectious agents in pigs causing late-term reproductive failure in sows and respiratory disease in growing pigs. Often, PRRSV infection is complicated by secondary bacterial infections being attributed to the immunosuppressive nature of the virus. Also, PRRSV viremia lasts for weeks, and virus then still can be detected in lymphoid organs for several months, demonstrating difficulties or failure of the host's immune response to clear the virus (Allende et al., 2000).
There are two distinct viral PRRSV genotypes causing similar clinical symptoms that diverge by about 40% on nucleotide sequence level, genotype I (EU) and genotype II (US). The North American (US) prototype strain is VR-2332, while the European (EU) prototype strain is Lelystad virus.
A growing number of infectious cDNA clones of the PRRS virus are becoming available to the scientific community, most of which are based on the US type of the virus. For the EU type, however, only one clone is published and has been used for basic research studies whose sequence is derived from Lelystad virus isolated in 1991.
Thus, there is a strong need for new infectious cDNA clones of European (genotype I) PRRS virus, for a better understanding of PRRS, for reproducing said disease in its different forms, for comparative tests, and as platform for the development of new vaccines, medications and diagnostics for the prophylaxis, treatment and diagnosis of PRRS.